ARRL Satellite Bulletin ARLS002 (2004)

SB SPACE @ ARL $ARLS002
ARLS002 AO-40 Still Ailing
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Space Bulletin 002 ARLS002
From ARRL Headquarters
Newington, CT January 29, 2004
To all radio amateurs
SB SPACE ARL ARLS002
ARLS002 AO-40 Still Ailing
Ground controllers for the AO-40 satellite still are trying to
figure out just what happened aboard the spacecraft earlier this
week to cause a significant drop in the bus voltage. For now, the
satellite has gone silent in the wake of a precipitous voltage drop
from around 26 volts down to 18 volts early on January 27 (UTC).
AO-40 controllers are fairly certain that one or more shorted
battery cells are at the root of the problem. Efforts to restart the
satellite's 2.4-GHz downlink transmitter so far have been
unsuccessful.
"Our current best understanding is that we suffered a catastrophic
failure of the main battery, which is clamping the bus voltage at a
low level," Stacey Mills, W4SM, of the AO-40 command team said in a
posting on the AMSAT-DL Web site.
The AO-40 ground team is sending blind commands to the spacecraft to
activate its onboard computerized control system in order to switch
in the auxiliary battery bank, which was tied to the main battery
bank after a bus voltage drop January 26, and disconnect the main
battery.
Mills said that while ground controllers don't claim to fully
understand what happened aboard AO-40, operator practices were not
to blame.
"AO-40 was designed to withstand all that you can throw at it," he
said. "Although there was a lot of passband activity on Sunday--and
under really marginal conditions heavy usage could put us
transiently in a negative power budget--it is now clear that it was
the failing of another cell on the main battery that caused the
passband shutdown at that time."
Mills explained that the main AO-40 batteries consist of 20 40-Ah
cells arranged on three of the radial support arms inside the
spacecraft--two packs of seven cells and one pack of six cells.
"It is entirely possible or even probable that the main batteries
suffered some damage during the 400-N motor event," Mills said,
referring to the onboard catastrophic incident that caused AO-40 to
go dark and destroyed some onboard systems less than a month after
its launch in November 2000.
"If it's at all possible to bring AO-40 back, we will," said Mills,
who concedes that he's "lived and breathed AO-40" for more than four
years. "No success for even weeks or months does not mean that we
won't eventually be successful. We will sure keep trying."
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